1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same, in which an interlayer insulating film having a low dielectric constant is formed so as to coat a wiring and either a via hole or a contact hole is formed in the interlayer insulating film.
2. Description of the Prior Art
Recent years, as a semiconductor integrated circuit device has come to be more highly integrated and denser, accelerating of a data transfer speed has been demanded. For this reason, a low dielectric constant film offering little RC delay is used. Examples are a SiOF film having a relative dielectric constant of 3.5 to 3.8 and a porous SiO2 film having a relative dielectric constant of 3.0 to 3.1.
On the other hand, wiring materials are changing from the conventional aluminum (Al) to copper (Cu) with low electric resistance.
An insulating film having a low dielectric constant (hereinafter referred to as low dielectric constant film) is formed on a copper wiring, and after this a via hole is formed in the low dielectric constant film. At this time, a block film for protecting the copper wiring is required in order to prevent the copper wiring from being oxidized and etched. Conventionally, a silicon nitride film (hereinafter referred to as SiN film) has been used as the block film.
However, there exists a problem that a relative dielectric constant of the SiN film is as high as about 7.
Alternatively, as the block insulating film, use of a SiC film formed by a plasma enhanced CVD method has been conceived. Although a relative dielectric constant of the SiC film is about 5 which is relatively low, the SiC film is accompanied with a problem of a relatively large leakage current which results in generation of leakage current between wirings that sandwiches a interlayer insulating film.
It is also preferable for the block insulating film to have a function of preventing the diffusion of ingredients contained in the wiring (e.g. copper) to an interlayer insulating film.
The object of the present invention is to provide a semiconductor device capable of preventing oxidation and etching of a wiring, when an interlayer insulating film having a low dielectric constant is formed so as to coat the wiring and when a via hole or a contact hole is formed in the interlayer insulating film. Another object of the present invention is to provide a method of fabricating the semiconductor device. Yet another object of the invention is to provide a semiconductor device capable of reducing leakage current between wirings sandwiching an interlayer insulating film and a method of fabricating the same. Still another object of the invention is to provide a semiconductor device capable of preventing the diffusion of ingredients contained in the wiring to an interlayer insulating film, and a manufacturing method thereof.
According to a method of fabricating a semiconductor device of the present invention having an interlayer insulating film formed on a wiring, a silicon compound containing only silicon (Si), oxygen (O), carbon (C) and hydrogen (H) is converted into a plasma gas to react itself, thus forms a block insulating film containing Si, O, C and H between the wiring and the interlayer insulating film.
Since the silicon compound containing silicon (Si), oxygen (O), carbon (C) and hydrogen (H) is used and oxidizing agent is not used, a lower wiring, a copper wiring for example, can be prevented from being oxidized when the block insulating film is formed. Moreover, since the lower wiring has been already coated with the block insulating film when the interlayer insulating film is formed, the lower wiring can be prevented from being oxidized even if oxidizing agent is used in forming the interlayer insulating film.
Incidentally, the interlayer insulating film having a low dielectric constant is generally porous, and moisture tends to permeate the lower wiring from the outside through the interlayer insulating film. On the contrary to this, in the case where the block insulating film is formed between the lower wiring and the interlayer insulating film having a low dielectric constant, even if the moisture permeates from the outside through the interlayer insulating film, the block insulating film prevents the moisture from reaching the lower wiring. Thus, corrosion of the lower wiring can be prevented.
Moreover, by sandwiching the block insulating film between the lower wiring and the interlayer insulating film, a ingredient of the lower wiring, such as copper, is prevented from diffusing into the interlayer insulating film from the lower wiring. Thus, leakage current between the wirings sandwiching the interlayer insulating film can be reduced. In addition, a dielectric constant of the whole interlayer insulating film can be reduced since the block insulating film occupies only a fraction of the entire interlayer insulating film.
Furthermore, in the case where an opening portion reaching the lower wiring is formed in the interlayer insulating film, the interlayer insulating film formed on the lower wiring is first etched by using a photoresist film as a mask. At this time, etching is stopped so as not to etch the block insulating film. Subsequently, the block insulating film is etched after the photoresist film used as a mask is removed. With such etching, since the lower wiring is not exposed to an ashing gas and an etching gas for removing the photoresist film, ion bombardment to the lower wiring can be minimized to suppress etching of the lower wiring and oxidation thereof.
The block insulating film may underlaid with a sub block insulating film which is formed of a thin insulating film with a high relative dielectric constant and a high density. This sub block insulating film is formed of either a thin insulating film containing C and H or a thin insulating film containing Si and C. In this specification, the block insulating film formed on the sub block insulating film is referred to as a main block insulating film. Specifically, the block insulating film is a two-layered structure composed of the main block insulating film and the sub block insulating film. With such two-layered structure of the block insulating film, even if the sub block insulating with a high density is used, a dielectric constant of the whole interlayer insulating film can be reduced together with reducing leakage current.
A film with a high density can be formed in the following manner. For example, a plasma film-forming apparatus of a parallel plate type is used, and a power source of a low frequency and a power source of a high frequency are connected respectively to a lower and upper electrodes of the apparatus, and the supplied power of the low frequency is not higher than the supplied power of the high frequency.
Furthermore in the case of forming a block insulating film having a low dielectric constant, it is advantageous to use a compound having a siloxane bond (Sixe2x80x94Oxe2x80x94Si) as the silicon compound. This is because silicon (Si) contained in the silicon compound already bonded with oxygen (O) in the form of a siloxane bond, which makes the leakage of current smaller.
Furthermore, in the case of using the compound having the siloxane bond as described above, it is advantageous to set a spacing between the lower and upper electrodes equal to 25 mm or lower. Narrowing the spacing increases a sheath region generated between the electrodes. As a result, the decomposition of the compound having a siloxane bond is facilitated, and a methyl group or the like contained in the film is reduced, thus making the film dense.
Similarly, when a power of 2/xcfx80(W/cm2) or higher is applied to the substrate, decomposition of the compound having a siloxane bond is facilitated, which in turn forms a dense film.